Configuration of the C(20) epimer of 7,8-dihydrobatrachotoxinin A

7,8-Dihydrobatrachotoxinin A is an intermediate in the synthesis of batrachotoxin, the extremely potent venom from the Colombian frog Phyllobates aurotaenia. A crystal structure analysis by x-ray diffraction has confirmed that the intermediate is identical with the natural batrachotoxinin A except for the saturation of the C(7)-C(8) bond. There are seven asymmetric carbon atoms in the molecule. The cis A/B and C/D ring junctions cause the molecule to assume the characteristic shape of cardioactive steroids. A cage is formed from the A-ring, atom C(9), and the O atom that makes the ether linkage between C(3) and C(9).